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Abstract
New data are presented relating to deeper levels in the Falun Mine, providing new insights into the problems of ore genesis. The new data, combined with previous results, can be interpreted in the following steps of evolution: (1) volcanism and sedimentation creating the Leptite Formation, (2) folding prior to, and after, the intrusion of older granites and acid and basic dikes (“felsit” and “trapp” in older mining terminology), (3) faulting, causing displacement of the dikes and folding in restricted blocks, (4) emplacement of sulphides forming compact bodies of pyrite with irregularly distributed chalcopyrite, sphalerite and galena. Apparently, this mineralization was combined with the alteration of the leptites (acid metavolcanies) into “ore quartzites” (metasomatically altered leptites) and the formation of “sköl rocks” (biotite, chlorite, muscovite, talc, anthophyllite, some cordierite). Rich copper ores (“sköl ores”) were formed when “sköl” rocks were mineralized by chalcopyrite. At the same time, ore solutions were probably transported along joints (“släppor”) accompanied by impregnations and veinlets of chalcopyrite in “ore quartzites”. Where the copper content was sufficiently high such mineralizations could be mined (“hard ores”). It is clear that the emplacement of the compact ores postdates the faulting. It is proven that the formation of the Falun ores, at least, as they appear today, does not have any direct relation to the volcanism that created the Leptite Formation.